Femtosecond laser welding boosts solar cell recycling
Researchers in the US have used a femtosecond laser to form glass-to-glass welds to make solar panels easier to recycle.
The proof-of-concept study at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) shows that using a femtosecond laser for welding would eliminate the need for plastic polymer sheets that are now laminated into solar modules but make recycling more difficult.
At the end of their useful lifespan, the modules made with the laser welds can be shattered and the glass and metal wires running through the solar cells can be easily recycled while the silicon can be reused.
“Most recyclers will confirm that the polymers are the main issue in terms of inhibiting the process of recycling,” said David Young, senior scientist and group manager for the High-Efficiency Crystalline Photovoltaics group in the Chemistry and Nanoscience department at NREL.
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A femtosecond laser from Trumpf uses a short pulse of infrared light that melts the glass together to form a strong, hermetic seal. The glass weld can be used on any type of solar technology—silicon, perovskites, cadmium telluride—because the heat of the weld is confined to a few millimeters from the laser focus.
Solar modules are made of semiconductors designed to capture a specific portion of the solar spectrum, harnessing sunlight to create electricity. Typically, the semiconductors are sandwiched between two sheets of glass laminated together with polymer sheets.
“As long as the glass doesn’t break, the weld is not going to break,” said Young. “However, not having the polymers between the sheets of glass requires welded modules to be much stiffer. Our paper showed that with proper mounting and a modification to the embossed features of the rolled glass, a welded module can be made stiff enough to pass static load testing.”
NREL’s research is the first to use a femtosecond laser to form glass/glass welds for use in a module. A different type of edge sealing using nanosecond lasers and a glass frit filler was tried in the past, but the welds proved too brittle for use in outdoor module designs. The femtosecond laser welds offer superior strength with hermetic sealing at a compelling cost.
The paper, “Towards Polymer-Free, Femto-Second Laser-Welded Glass/Glass Solar Modules,” appears in the IEEE Journal of Photovoltaics.
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